Silo construction



May l, 1951 w, G, MAR-HN 2,551,217

SIL-0 CONSTRUCTION Filed April 17, 1946 :5 Sheets-511x661'. l

v 244 5 Z/ 5 i@ J i l 5 y ZZ May l, 1951 w. G. MARTIN SILO CONSTRUCTION 3Sheets-Sheetv2 Filed April 17, 1946 ay l, 1951 w. G. MARTIN SILO CONSTRUCTION 3 Sheets-Sheet 5 Filed April 17, 1946 Patented May l, 1951 sILo CONSTRUCTION Wesley G. Martin, Milwaukee, Wis., assignor to A. 0. Smith Corporation, Milwaukee, Wis., a

corporation of New York Application April 17, 1946, Serial No. 662,854

12 Claims.

This invention relates to an improved silo construction and has been employed in connection with a substantially airtight glass-lined steel silo in which the pressure inside the silo is maintained at approximately atmospheric when silage is confined therein.

It has been found that in a silo of generally airtight construction there is a considerable change of temperature between the nighttime and daytime hours. Also there are changes or differences in temperature in such a silo between the various seasons of the year. These differences of temperature, such as between day and night, result in changes in pressure of the atmosphere inside the silo. With these pressure changes the silo is said to breathe so that at certain periods air tends to flow into the silo due to the decrease of pressure within the silo compared to the pressure of the atmosphere outside. At other periods the pressure within the silo is greater than the atmosphere around the silo with the result that air and gases tend to flow out of the silo to the atmosphere. f f

Under such conditions even in a silo of generally airtight construction there may be pinholes and cracks through which air can flow into the silo and a fresh supply of oxygen would be regularly supplied to the silage. Such fa constant flow of oxygen tends to promote mold growth and deterioration of the silage.

The present invention is directed toward a substantially airtight silo in which a pressure or expansion chamber takes care of thetendency of the air to flow in and the gases to flow out of the silo under volume changes of the gases confined in the silo. The pressure chamber employed is one which can vary its volumein oifder to maintain substantially atmospheric pressure within the silo at all times.

Under the invention such small amounts of oxygen come into the silo that the silage is most perfectly preserved.

The principal object of the invention is to provide a slio in which the pressure inside the silo is maintained at substantially atmospheric at all times regardless of normal volumetric changes.

Another object is to provide a silo in which mold growth with consequent deterioration of the silage is substantially prevented.

A further object is to provide a silo in which provision is made for the silo to breathe without any substantial change in the atmospheric pressure inside the silo and without mixture of air with the gases inside the silo.

adjusting the yblower pipe, or for any other rea` SOIL Another object is to facilitate blower filling of an airtight silo.

Another object is to improve the appearance of the silo.

Other objects and advantages of the invention will appear in the following description of an embodiment of the invention illustrated in the accompanying drawings. In the drawings:

Figure 1 is a longitudinal elevation of a silo with parts broken away and sectioned with the diaphragm in a deflated position;

Fig. 2 is an enlarged elevational view, partly in section, of the bottom portion of the silo;

Fig. 3 is an enlarged View, partly in section, of the upper portion of the silo with the diaphragm hanging down within "the silo or in a defiated position;

Fig. 4 is a view similar to Fig. 3 with the diaphragm pushed upwardiy in an inflated position; and

Fig. 5 is a top plan View of the diaphragm in a deated position.

The silo shown in the drawings to illustrate the invention is in general similar to that disclosed and claimed in the application of the present inventor entitled fSilo, Serial No. 598,044, led June 7, 1945 and assigned to the assignee ofthe present application. The silo comprises a plurality of cylindrical sections I located one on top of the other and secured together at circumferential joints 2. The silo is closed at the top by cover 3 and rests on a conically shaped foundation 4 of cement or the like embedded in the ground a substantial depth beneath the silo shell.

The sections I are each of suitable gauge metal rolled to cylindrical shape and welded along a longitudinal seam. Each section l is preferably lined upon fabrication with a ceramic enamel coating 5 to protect the metal from corrosion and the coating 5 may also be applied to the outside surface of the silo.

An opening is provided in the bottom section l which is closed by airtight door 6 to give access to the inside of the silo for clean-out purposes and the like. The silo ller pipe 'l extends upwardly inside the silo wall and curves inwardly from the wall adjacent the top section I. The pipe 1 is suitably secured to the silo shell and is closed at the outer end with the airtight cover 8 when not in use. The joint between pipe I and the silo wall is also sealed to prevent leakage of air into the silo.

The circumferential joints 2 arefconstructed in a manner to provide airtight joints between sections I. The joint construction described andrw,y

claimed in the application above referred to may well be employed.

The silage is removed from theebottorrr'of the. silo by any suitable mechanicalmeanszthat will prevent flow of air therethrough into the silo when silage is being removed.

The means shown in the drawings is the same as that described and claimed in the application above referred to. An auger or screw 9 extends to the bottom ofthe silo throughadiagonal opening infoundation 4 andthe outer end of the auger extending from the foundation isenclosed in casing I0. Silage moved out of the silo by screw 9` is discharged through pipe II- extending downwardly from the outer end of casing I0. The door I2 is disposed as-an airtight closure for pipev II when silage is not being discharged.

The screw 9` is` rotated by gasoline engine I3 through suitable gearing and a speed reducer It. The inner endof screw 9 is gear connected to a second auger or screw I5 and the latter is driven around the foundationll-.when screw 9 is rotated by engine II. The screw I5 also revolvesand is formed to cut upand,loosen the silagefor ready removal by screw 9.

Oxygen-free gas may be suppliedto the inside of the silo by the exhaust gases of engine I3. The exhaust gases help prevent entry of air during removal of silage and maintain a favorable pressurecondition inside thesilo. The employment of the exhaust gases will be describedmore fully hereinafter.

The exhaust gases of engine I3 are piped through a lter IB-.and then-are carried to the pipe I'I by the pipe I8. The pipe I1 extends substantially. to the top of the siloy on thefinsideof the -silo wall andv is connected to pipe I8 by cour pling IQ. Pipe I8 is in turn connected to the engine exhaust manifold.v through filter I6. P-ipe I'I not only serves to'carry oxygeniree gasesrinto the silo, but when coupling I9 is removed, asat the time of lling the silo, air driven into the silo in the filling operation ows out. through pipe I'I. When filling iscompletedcoupling I9 is replaced and thev exhaust gases can then. flow through Apipe IT and l-fromengine I3.

The lter I6 may be constructed to operate as a container to trap condensate from tlieexhaust gases formed in the passage of the gas through pipes I'I and I8 into the silo. Itmay also be Well to employ a water trap, not shown, in the pipe line after it leaves the lter toY catch condensate from the exhaust gases.

The exhaust gases or other gases that are used may be carried into the siloin other ways than that shown and other means forsupplying oxygen-free gas may be employed. For example the screw 9 may be driven by an electric motor and nitrogen gas supplied to the silo from a storage tank. The exhaust gases may-also bepumped directly into the bottom of the silo.

The exhaust gases from engine I3 or other oxygen-free gases piped into the silo replace in substantially equal volume the volume of silage removed. The engine I3 is provided with a clutch, not shown, so that exhaust gases may be supplied to the silo without driving screw El.

The silo is provided with an expansion chamber which may be assembled with the silo in a number of different ways. The expansion chamber may be located outside the silo and be connected thereto Aor be provided inside the siloitself.

One type ofiexpansionr chamber construction, as shown in the drawings, which permits the silo to `breathe without mixing fresh air with the gases inside the silo, has a diaphragm 2B which hangs looselysuspended within the top of the silo below the silo top 3 to provide chamber 2| therebetween. Diaphragm 20 may be a cloth impregnated with rubbenorfl'exible-,resin to prevent passage of air therethrough. A thin metal diaphragm might alsocbeemployed.

The upper section I and the cover 3 are provided with the complementary flanges 22 and the circumferential vperiphery of diaphragm,.20 is secured'between flanges 22 when cover dome 3.is,assembled on top of the top section I and secured thereto-by. a plurality of bolts 23. Rubber cementor the like may be employed to seal the joint between the top 3 and the upper sectionI. The diaphragm is `of 'a size with respectv toexpansion chamber 2.Iy so that when the diaphragm is up or inflated` it will strike the top of the silo before it is under tension. This will conserve the diaphragm.

Arweather-proof vent 24, which may comprise a short pipe suitably covered at the outer end for protection from the elements, is secured to top,3 'to permit air to flow in and out ofchamber 2l formed between diaphragm 2i) and top 3.

A relief valve 25' which may bea liquid or mechanicalvalve is disposed on` one side ofthe silo at a level where it may be readily observed. The valve 25 may be connected to the silo in a number of different ways and is provided to let gasesow out of the silo or air, flow into the silo upon increases or decreases of the temperature within the silo effecting. extraordinary expansion and contractionof the gases insidethe silo.

The relief valve 25 shown in the drawings isa liquid seal and comprises a U shaped.tube ofv generally large bore connected to the'sma-ll bore pipe IS carrying gasesfrom engine I3 to pipe II extending upwardlyV withinv the silo.

One end of the tubev or valve;25` is connected directly into pipe Il and the other end isturned downwardly and is open. Each side of the U tube 25 is enlarged near the top tov provide a chamber 26 for receiving any liquid that would otherwiseV spill over by reason of increased air or gas pressure. The liquid in the tube is of a non-freeze-type, and due to the large bore of the tube, air or gases as ,the casegmay be, will bubble through the tube when the'liquid is forced substantially fully into either side of the tube.

Under ordinary conditions, as will be described hereinafter, valve 25 will prevent the passage of gases and air therethrough, but it is provided as a safety measure'totake care of extraordinary breathing by the silo.

The valve 25, has another function and that is to serve asa pressure indicator to enable the operator to determine whether diaphragm 2U is up or down.. If 'valve 25is of a construction that it cannot be employedas a pressure indicatorthen a separate indicator may be installed.

After the silo is initially lled with the fodder which is to be convertedV into silage, the diaphragm 20 will ordinarily be in a deated position and hanging down within the silo. Air may flow into the silo through the relief valve for` through relief valve 25, if diaphragm I8 reaches maximum iniiation while the gases within the silo are still expanding or increasing in volume.

At the time when silage is to be removed from the silo it may be that due to pressure conditions inside the silo diaphragm 2U will be in a deflated position. This can be observed on relief valve 25. Also when door I2 to discharge pipe II is opened pressure inside the silo is released and diaphragm 2i! tends to deflate.

The ordinary procedure followed by the operator before removing silage will be to start motor I3 declutched from screw 9 to warm up the engine. As soon as the motor is started exhaust gases are driven into the silo through pipes i3 and Il. The exhaust gases inate diaphragm 2D, should it be deflated, and tend to prevent it from deating when discharge door I2 is opened.

After engine I3 is warmed up it is clutched to drive screw 9, door I2 is opened, and the screw forces the silage out through discharge pipe II.

yAfter withdrawal of silage is completed door I2 is closed and engine I3 is declutched from screw 9. Relief valve 25 is then observed by the operator. If the liquid level therein indicates that diaphragm 20 is down engine I3 is run to produce exhaust gases which are driven into the silo through pipes I8 and I 7. The exhaust gases are forced into the silo until'diaphragm 20 is at maximum height or inflated as determined by the level of the liquid in relief valve 25. The cycle of operations here described is ordinarily carried out every time that silage is removed, as the diaphragm 20 should be at maximum height when removal of silage is completed and also should be inflated when silage is being removed, to maintain the atmospheric pressure conditions inside the silo that are desired.

^ The temperature inside a silo which is constructed to be airtight ordinarily will rise during the day and decrease during the night. As the temperature rises the gases inthe silo expand and the pressure inside the silo will rise above atmospheric pressure and the gases will tend to flow out of the silo unless an expansion chamber is provided. When the temperature lowers the gases in the silo contract and the pressure inside the silo will lower below atmospheric pressure and air will tend to flow into the silo unless an expansion chamber is provided. Under these conditions the oxygen tends to promote mold growth, and deterioration of the silage is likely to result. The plant tissue and bacteria cannot use up an unlimited constant supply of oxygen without deterioration of the silage.

Under the present invention, however, the pressure inside the silo proper remains substantially at atmospheric pressure at all times as the expansion device which here is shown as the diaphragm 20 operates to maintain atmospheric pressure within the silo.

Ordinarily during the day diaphragm 20 isinated as the pressure rises with rise of temperature, and air in chamber 2I is forced out of vent 24. During the night as the temperature lowers the gases within the silo contract and diaphragm 20 is deflated or forced inwardly as air moves through vent 24 into chamber 2l. Changes of pressure and the consequent volumetric changes of the gases within the silo under rdiiferent temperature and barometric conditions is thus taken care of by the diaphragm 20 without permitting air to enter into the silo proper and mix with the gases therein.

The chamber 2I is of large area so that the space traversed by the diaphragm 20 is suflicient to take care of the breathing in a silo when the silo is nearly empty and temperature changes are at a maximum. The diaphragm 20 being of flexible material is capable of moving inwardly of the silo a substantial distance when the air tends to flow into chamber 2|. However, relief valve 25 is provided to let air flow into the silo proper under extreme or unusual temperature changes, where the diaphragm would be stretched beyond capacity or possibly under conditions where diaphragm 20 is unable to expand due to contacting the silage at the top of the silo. Under these conditions air would flow into the silo through the valve 25 before the diaphragm 29 would break or the silo collapse.

In the case where the diaphragm may be hampered by the silage when the silo contains a large mass of silage and temperature changes therein are little if any, the complete exclusion of air is not so important as in the case of maximum changes of temperature and a small volume of silage because limited amounts of oxygen can be absorbed and converted into CO2 and H2O by the plant cells and bacteria without producing mold growth and deterioration of the silage.

The pressure or expansion chamber which may be employed serves to provide an accumulator to maintain atmospheric pressure inside the silo proper at all times so that the oxygen in contact with the silage is positively limited. The airtight construction of the silo insures that the diaphragm will operate effectively and that the oxygen supply inside the silo will be limited to an amount that the plant growth and bacteria will absorb before mold growth can thrive.

The invention provides a silo construction in which entry of air or oxygen is prevented when silage is being removed and during the breathing cycles that the silo goes through under temperature changes between day and night or different seasons of the year. The pressure or expansion chamber insures that the silage will be most perfectly preserved as entry of air into the silo in contact with silage is substantially eliminated.

Various embodiments of the invention may be employed within the scope of the accompanying claims.

I claim:

1. In a storage structure, a silo of airtight construction formed of a generally cylindrical large diameter metal body member closed at the top by a cover having an opening therethrough to the inside of the silo, an expansion chamber in the top of the silo to maintain atmospheric pressure Iwithin the silo under all operating condiu tions and bounded by the top of the silo on one side and on the other side by a substantially flexible impervious diaphragm suspended within the top of the siloand norm-ally spaced in` 1, 'wardly thercfrom: to 'separates said silo intor.,a closed 'inner.' chamber: irnwhich the silage.. isle-1 cated andi theHex-pansion:chamber;open;.to .ther-s atmosphere;J and said# diaphragm being: disposed toinnate: uponv expansionaofi gasesiiwithinthe. silo and deiiate upon'contractionof thesiloigases and know' ofi air into? said` expansion.: chamber ,to

maintain atmospheric'pressure within'zthe silo under substantially:` all operating.. conditions;

2. I'n al storage structure: a silo of' airtightV constructioni comprising .a generally cylindrical.

large diameter metalbody': member closed at. the top by a cover having an opening therethrough to Ythe'linside of thesil,V an.. expansion chamber inf the -topy of the 1 silo'v tol maintainffatmospheric pressure within the silo .under all operating con;

ditions'andfbeundedbylthetop of thesilo on one side and on the.V otherside by -a` substantially(-y flxible impervious diaphragm suspended within 'thetop Jof the*I silo; and i normally f spaced inwardly-therefrom. to iseparate said silo into a closedinner chamber in which the silage is located and the expansionlchamber open tof the atmosphere, said diaphragm: being disposed: to:

mit flow of air. into the silounder extraordinany.Vv breathing of! the silo' with .which the' diaphragm' expansionchamb'er is-..Lmable to cope..

3. In.` a storage structure, a silo of airtight construction comprising a. generally cylindricalY largel diameterfmetal body member.' closed at.

theitop bya cover having-van` opening there# through Ito the Vinside 1voi the silo, an. expansion chamber. inthe-top ofthe silo to maintainatmosphericfpressure 1 within the silo under. all operating conditionsand bounded by the tcp ofV the..silo on one sideandon the otheriside' by a substantially flexible i impervious' diaphragm suspended within thetop of thesilo andv normally spaced. inwardly therefrom to separate t said :silo intoaclosed inner chamber iniwhichzthe silage islocatedand the expansion chamberopen to thev atmosphere, saidr diaphragmbeing disposed to' inflate uponexpansion of gases within thesilo and. delateupon contraction of the silo gases and flow of air into said expansion chamber to main tain atmospheric pressure within the silo under substantially all operating conditions, a pipef secured within the silo and projecting fromthe lower end thereof, a source of; oxygen-free gas connected to said pipe for supplying purging gases within the silo to maintain atmospheric pressure withinrthesilo-andpurge oxygen therefrom; a relief valveconnected to the extension.

of said'pipe locatedvoutside said'silo and set for predetermined pressure I conditions to release' gases from the silofandA permit yow oi lair into,-

the silo'under extraordinaryv breathing of the silo withwhch the diaphragm pressure cham berisunableito' cope and means in said valve'A to' indicate-whether the saiddaphragm is up or down.I

4. Ina storage structure. `.asilo Aof Vairtight con-- struction, formed-:oliy a; plurality of 'superimposed cylindricallsections closedaat the,top by a cover member having an'Jopeningftthe inside of the silo;;a1iiexible diaphragmsuspendedfrom thetop. v of: thesilo tozseparatefthesilo intoachamberin which silage* iszstored'. substantially free. of: contactzwithzair and afchamber'openv to the air through-1 the'openingf; in said cover, andy said. diaphragm;beingfsubject to ination bythe exe'- pansion of gasesfwithin thesiloand deationby contraction'of the gaseswithin the silo, apres-l sure indicator connected-to Vthe. silo, means there inA to indicateV whetherY said.- diaphragmis inflated or deflated, anda sourcev of' oxygen-free gas .connected to -thefslo to 'introduce oxygen-free gasintdsaidfsilo toinflate said diaphragmY if said` indicator indicates deationthereof t0 thereby maintainsubstantially atmospheric pressure withincthe silo fand rprevent the silo from` collapsing or burstingi'while remaining free of air in contact-with the silage.

5.` A metal silage'zstorage` container of' sube stantially airtightaconstruction formed of a generally cylindrical large'diameter body: member closed at the-top by'a' cover having Aan opening therethroughY to tli'e'finside' of the containena flexibleV impervious` diaphragmv suspended. be

neath said cover andl normally spacedtherefrom-v within the-top'of the container, saddiaphragm being'of substantially thediameter oiv thecontainertolseparate the vsame into an inner chamber inwhichsilageis. storedxfree from contactI with air and an outer chamber between the diaphragm 'and cover exposed -tofthe entryofVV air through the-opening insaidcover, said diaphragm expanding'v outwardly of the container under pressure of" gases inside 'the silowandto expand inwardlyof the-container under'pressure: of air.

outside: the container toifprevent the container from bursting:@collapsing-under changes ofpres'sureetherein, annunloading device connected to :the bottom othef-container: tofunloady silage from .the bottom thereof-withoutanyy substantial entry' ofainfand" afsourcef'of oxygen-free gas connected :to the-inner chamber of the container to supplyroxygenreegas'thereto to inatesaid' diaphragmfupon'loss-vof pressure` upon the removal of silage'.V

6. -AA metal silage storagefcontainer of substantially.' airtight constructionior1ned of Y a generallyV cylindrical large 'diameterf body member closed atfthetop-by; alcovenmemberhaving an opening therethrough to zthe inside of thereontainer;:a flexible-impervious Idiaplfxragm suspended' beneath saidr'coverfandnormally spaced there-l from within',v the Ytop 4of* the container, said dia-` phragm` beingxo'f substantially` the diameter of the containerfto'separate-the same'into an inner chamber; inwhichsilageds -stored free-from' con-4 tactfwthair and anouter chamberbetween thediaphragm-andcover exposed to the` entry.- of air throughtheopening in said-cover, said diaphragm?expandingmutwardly -of the container underfpressurefo gases-inside the silo and tov expand. inwardly ofthe container under pres-Y sure of air: outside thei containerV to prevent the container.I froml burstingv orcollapsing under changesrofir pressuresthereim an unloader con-` nectedfinto the bottomfI of ,thefcontainen a gasoline enginerfconnected tothe' ,unloader to' drive thersame for :removaL of y silage fromi thef bottoml ofA the; silo,'and:.a connectionfbetween the ex'- haustfa of theV engine fand .the'inner'chamber'of then-silo :to :carry: exhaust #gasesfathereto fto maine tain the diaphragm inatedl-duringrremoval of Y9 silage and prevent any substantial entry of air or to inate the diaphragm if the same is deflated.

7. A metal silage storage container of substantially airtight construction, an auxiliary pressure accumulator bounded by a solid structure open on one side to the atmosphere for receiving air forced therein by atmospheric pressure and having an expansion member exposed to gases on the inside of the container and the air in the chamber on the other side, said expansion member being operated by the pressure of the gases on the inside of the container and the air on the outside to decrease or increase, respectively, the capacity of the chamber for holding air to keep the container from bursting or collapsing under changes in pressure, an unloading device connected to the bottom of the container to unload silage from the bottom thereof without any substantial entry of air, and a source of oxygen-free gas connected to the inside of the container to supply oxygen-free gas thereto to expand the expansion member upon loss of pressure in the container upon the removal of silage.

8. A metal silage storage container of substantially airtight construction, an auxiliary pressure accumulator bounded by a solid structure open on one side to the atmosphere for receiving air forced therein by atmospheric pressure and having an expansion member exposed to gases on the inside of the container and the air in the 1 chamber on the other side, said expansion member being operated by the pressure of the gases on the inside of the container and the air on the outside to decrease or increase, respectively, the capacity of the chamber for holding air to keep the container from bursting or collapsing under changes in pressure, an unloading device connected to the bottom of the container to unload silage from the bottom thereof without any substantial entry of air, a gasoline engine connected to the unloading device to drive the same, and a connection between the exhaust of the engine and the container to carry exhaust gases thereto to maintain the expansion member expanded during removal of silage and prevent any substantial entry of air or to expand the expansion member should the same contract in service.

9. In combination, a thin walled metal air tight silo structure of generally large upright cylin- .drical construction with a closed top therefor and subject to collapse or rupture under a small pressure differential between the outside and inside thereof, a foundation supporting said structure and closing the bottom thereof, a normally closed inlet for filling the structure with material to be stored therein, a normally closed discharge opening at the bottom of the structure for periodic removal of material stored therein, said silo structure being normally exposed to the out-ofdoors and subject to breathing under conditions of temperature change between day and night and between seasons of an order capable of collapsing or rupturing the same, said silo structure having a bleeder opening therein normally opening above the level of material in the silo, and a flexible walled expansion member secured to said structure and sealing said bleeder opening to thereby separate the gases enveloping the material in the silo from the atmosphere, said expansion member constituting at least a partv of an expansion chamber free to expand and contract in volume under differences in pressure between the gases inside the silo and the atmosphere, whereby the silo structure is protected from injury and the maintaining of an 10 air tight silo structure is facilitated at all times.

10. In combination, a thin walled sheet metal air tight silo of the class described constructed of metal sheets of a thickness and weight generally incapable of withstanding the maximum pressure variations in the free gas space of the silo during normal use thereof, said silo having sealed joints between the sheets and being adapted to be exposed to varying temperature conditions of the outside atmosphere tending to vary the pressure conditions of the free gas space above the stored material within the silo to the point of rupture or collapse, and a'flexible tension member sealing an opening in said silo and disposed to be subject on one side to the pressure inthe free gas space of said silo and on the other side to atmospheric pressure, said flexible member providing a volumetric expansion and contraction for the free gas space of said silo of suicient capacity to compensate for normal variations in volume thereof at substantially atmospheric pressure, whereby the free gas space of said silo is maintained at substantially atmospheric pressure throughout the normal use cycle of the silo and any tendency for breathing of air to and from the material stored in the silo is reduced to a minimum.

11. In combination, a thin walled sheet metal air tight silo of the class described constructed of metal sheets of a thickness and weight generally incapable of withstanding the maximum pressure variations in the free gas space of the silo during normal use thereof, said silo having sealed joints between the sheets and being adapted to be exposed to varying temperature conditions of the outside atmosphere tending to vary the pressure conditions of the free gas space above the stored material within the silo tothe point of rupture or collapse, a exible tension member sealing an opening in said silo and disposed to be subject on one side to the pressure in the free gas space of said silo and on the other side to atmospheric pressure, said flexible member providing a volumetric expansion and contraction for the free gas space of said silo of sufficient capacity to compensate for normal variations in volume thereof at substantially atmospheric pressure, whereby the free gas space of said silo is maintained at substantially atmospheric pressure throughout the normal use cycle of the silo and any tendency for breathing of air to and from the material stored in the silo is reduced to a minimum, and relief valve means connected to the silo and constructed to relieve emergency pressure conditions within the silo both positive and negative with respect to the atmosphere to protect the thin sheets of the silo against emergency loads beyond the compensating capacity of said expansion member and of an order capable of collapsing or bursting the silo.

12. In combination, an upright cylindrical air tight silo structure adapted to receive and store crop materials, a foundation supporting said s ilo structure and closing the bottom thereof, a discharge opening at the bottom of the structure for periodic partial removal of the material stored therein, mechanical means at the bottom of the structure for removing material through said opening, means to close said discharge open ing between periods of removal of material, and a iiexible expansion member connected to the silo structure and sealing a second opening therein to thereby separate the gases enveloping the stored material from the atmosphere, saidv expan- 

